Currently used mixing apparatus for mixing fibrous and powder materials may be exemplified by Omni mixers and Eirich Intensive mixers. The Omni mixer is an apparatus fitted with flexible rubber bowl on its oscillating plate without agitating blades, which performs mixing by diffusion by accelerating materials to be mixed and changing their speed and direction of movement, scattering them in random directions. The Omni mixer is suitable for batch mixing, but is not suitable for continuous mixing. The motion of the Omni mixer includes mixing by convection, shearing and diffusion. When a shearing force is applied to the material being mixed, the material may be damaged and if the fibrous material is fine, the fibers may become entangled during mixing, thus hindering uniform mixing of the fibrous and powder materials.
The Eirich Intensive mixer uses special blades in its cylindrical container and is suitable for mixing in batch but not for continuous mixing. In the Eirich intensive mixer, a load may be applied to the material and in the case of the fibrous material in particular, there may be problems such as damage to the material.
A pin-type continuous mixing apparatus, suitable for continuous mixing is described in Japanese Patent Laid-open No. 63-49238. However, this apparatus is directed towards adding liquid to powder and making it uniform, but not towards mixing the fibrous material and powder uniformly. Based on its structure of a plurality of mixing pins (having a ground face) fixed to a rotating shaft at right angles, it is not always sufficiently suitable for uniformly mixing fibrous material and powder material.
Other prior art includes the mixing apparatus disclosed in Japanese Patent Publication Nos. 59-51329 and 63-54416. However, in these apparatuses, a considerable load is applied to the material and, for example, if at least one of the materials has been semi-wetted, too much load is applied to the materials during mixing, throughout or locally, so that water is squeezed out of the semi-wetted material, thereby sometimes disturbing uniform mixing and damaging the material. Thus these apparatuses are not suitable for continuous mixing.
Although when mixing raw materials such as fibrous and powder materials, it is important to mix them uniformly without damaging the fibrous material, the apparatus described above may damage the fibrous material during mixing; therefore they are not suitable as apparatuses for continuously mixing fibrous and powder materials uniformly.